[Early effects of forest harvesting gap on understory plant diversity of three different plantations in Baiyun Mountain, China.] / 采伐林窗对白云山3ç§äººå·¥æž—æž—ä¸‹æ¤ç‰©å¤šæ ·æ€§çš„æ—©æœŸå½±å“.

Pinus massoniana, Cunninghamia lanceolata, and Phyllostachys edulis are the main afforesting species in the low hilly areas and valley of the southern Yangtze River for commercial purpose. Ecological problems such as the monotonous community structure and low biodiversity are common in these plantations. To understand the effect of forest harvesting gap on the understory plant diversity in the three plantations, different size gaps with identical habitats were conducted with cano-pies as control in the three plantations in Baiyun Mountain. The life form spectrum of plants and plant diversity were compared among the different forest gaps. The results showed that species richness was the highest in C. lanceolata plantation (57 species), followed by P. edulis plantation (53 species) and P. massoniana plantation (41 species) in two years after harvesting. In the early period, plant species were more abundant in the gaps than that in the controls in C. lanceolata and P. edulis plantations, but there was no significant difference between the gaps and the control in P. masso-niana plantation. The percentage of phanerophyte plants were significantly higher in the forest gaps covered 500 m2 area than that with other sizes. The percentage of the hemicryptophyte and therophyte plants were higher in the forest gaps covered 250 m2 area. The percentage of geophyte plants were higher in the forest gaps with 50 m2 area than the others. The resembling coefficients between the different size gaps were higher than that between the gaps and the control in the same plantation. The resembling coefficients between different size gaps in the same plantation were higher than that between different size gaps in different plantations. The resembling coefficients between the gaps and the control in different plantations were generally lower than the others. The species richness, Simpson ecological dominance index, and Shannon diversity index differed significantly for different size gaps. Except for Simpson ecological dominance index, the indices were significantly influenced by the plantation types. The effects of the interaction between plantation types and gap sizes on these indices were not statistically significant. Forest harvesting gaps altered life form spectrum of understory plants and increased plant diversity in the three plantations.

[Forest soil organic carbon density and its distribution characteristics along an altitudinal gradient in Lushan Mountains of China].

To understand the spatial distribution characteristics of organic carbon in northern subtropical forest soils along an altitudinal gradient in Lushan Mountains of China, six and five sampling plots with a 200-m interval of elevation and covered by different vegetation types were installed on the southern and northern slopes, respectively in July-August in 2010 to collect soil profiles, with the soil thickness, bulk density, organic carbon content, and organic carbon density of 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, and >40 cm layers measured. The soil organic carbon density was significantly affected by altitude and slope. On northern slope, soil organic carbon content increased with increasing altitude, and had significant negative correlations with soil bulk density and pH value. On southern slope, soil organic carbon content had no obvious variation pattern along the altitudinal gradient and had less correlation with soil bulk density and pH value, but soil organic carbon density decreased with increasing soil depth. The soil organic carbon density on northern and southern slopes was within the range of 7.07 - 10. 34 kg x m(-2) and 6.03 - 12.89 kg x m(-2), respectively. The larger variation of soil organic carbon density along altitudinal gradient and soil depth on southern slope suggested that the destruction of original vegetation and the establishment of forest plantation could be one of the important factors affecting the spatial distribution of soil organic carbon.

[Fine root biomass and its nutrient storage in karst ecosystems under different vegetations in Central Guizhou, China].

The degeneration of karst ecosystem is closely associated with the reduction of soil nutrients and fine root biomass, and the retention of soil nutrients is of significance in sustaining ecosystem functioning. To understand the changes in the fine root biomass and soil nutrient retention in degenerated karst ecosystems, a comparative study was conducted with three typical vegetation stands (forest, shrub, and shrub-grass) in Central Guizhou of Southwest China. Soil samples with fine roots were collected from the depths 0-5 cm, 5-10 cm, and 10-15 cm, with the related indices of fine roots and nutrients measured. In the three stands, fine roots dominantly distributed in 0 -10 cm soil layer, and decreased sharply with soil depth. The living fine root biomass in 0-10 cm soil layer under forest, shrub, and shrub-grass occupied 83.36%, 86.91%, and 93.79% of the total fine root biomass, and 42.78%, 56.75%, and 53.38% of the total living fine root biomass within the 0-15 cm soil layer, respectively. The fine root biomass of predominant plant species varied with vegetation types. The N and P storage of the living fine roots in 0-5 cm soil layer under forest stand was significantly higher than those under shrub stand and shrub-grass stand, and no significant differences were observed between the latter two stands. However, the N and P storage of the living fine roots in 5-10 cm soil layer under different stands decreased in the order of forest > shrub > shrub-grass (P < 0.05). There was a significant positive correlation between the plant aboveground biomass and the living fine root biomass in 0-10 cm soil layer, and a significant negative correlation between the N and P contents of plant leaves and the specific length of living fine roots, illustrating that the nutrient uptake and retention by the living fine roots could have particular importance in the aboveground biomass establishment and ecosystem functioning.